At present, for a DC-DC converter, a conversion mode includes a boost type, a buck type, and a buck-boost type, and an operational mode also includes a peak current mode, a valley current mode, and a voltage mode, which have a fixed frequency, and also includes a hysteresis mode which has a non-fixed switching frequency. As a load has increasingly high requirements on frequency components, a fixed switching frequency is essential, and is also critical. Therefore, a current-type DC-DC converter and a voltage-type DC-DC converter that have a fixed switching frequency are provided in the prior art. The current-type DC-DC converter has a buck type structure which works in a peak current mode. The current-type DC-DC converter controls on and off of a power tube through a current sampling circuit, a slope compensation circuit, and an error amplifier. Although the objective of implementing fixed switching frequency can be achieved, the current-type DC-DC converter has a relatively complex circuit structure, high cost, and undesirable anti-noise capability. The voltage-type DC-DC converter controls on and off of a PMOS power tube and an NMOS power tube by using an output level of a comparator, while the output of the comparator is determined by both a sawtooth wave with a fixed frequency and a level signal that is output by an error amplifier after error comparison and amplification of an output feedback voltage; however, because the error amplifier is used, large capacitance and large resistance are required to perform third-order compensation on an output direct current, so that the DC-DC converter has a complex structure and a large occupied packaging area in circuit integration, which increases the cost.
To sum up, an existing DC-DC converter can implement fixed switching frequency control of a power tube, but has undesirable anti-noise capability caused by a complex circuit structure, and has an excessively large occupied packaging area in a chip and increased cost in circuit integration.